Color conversion device and method of manufacturing the same

ABSTRACT

Responsive to image data of three colors, six hue data are obtained, and then first comparison-result data each relating to one of the six hues, and second comparison-result data each relating to one of the six inter-hue areas are obtained. Matrix calculation is performed on the first comparison-result data, and the second comparison-result data, using coefficients. By varying the coefficients, adjustment can be made to only the target hue or inter-hue area, without affecting other hues and inter-hue areas. Thus, the six hues and six inter-hue areas can be varied independently, and the large-capacity memory is not required. The coefficients used for the matrix calculation are stored in a storage, which can be set and altered by the use of a setting unit.

BACKGROUND OF THE INVENTION

The present invention relates to data processing used for a full-colorprinting related equipment such as a printer, a video printer, a scanneror the like, an image processor for forming computer graphic images or adisplay device such as a monitor. More specifically, the inventionrelates to a color conversion device for performing color conversionfrom image data in the form of a first set of three color data of red,green and blue, or cyan, magenta and yellow, to a second set of threecolor data of red, green and blue, or cyan, magenta and yellow. Theinvention also relates to a method of manufacturing the color conversiondevice.

Color conversion in printing is an indispensable technology forcompensating deterioration of image quality due to color mixing propertydue to the fact that the ink is not of a pure color, or thenon-linearity (in the hue) of the image-printing, and to output aprinted image with a high color reproducibility. Also, in a displaydevice such as a monitor or the like, color conversion is performed inorder to output (display) an image having desired color reproducibilityin accordance with conditions under which the device is used or the likewhen an inputted color signal is to be displayed.

Conventionally, two methods have been available for the foregoing colorconversion: a table conversion method and a matrix calculation method.

A representative example of the table conversion method is athree-dimensional look-up table method, in which the image datarepresented by red, green and blue (hereinafter referred to as R, G, andB) are input, to output an image data of R, G, and B stored in advancein a memory, such as a ROM, or complementary color data of yellow, cyanand magenta (hereinafter referred to as Y, M, and C). Because anydesired conversion characteristics can be achieved, color conversionwith a good color reproducibility can be performed.

However, in a simple structure for storing data for each combination ofimage data, a large-capacity memory of about 400 Mbit must be used. Forexample, even in the case of a compression method for memory capacitydisclosed in Japanese Patent Kokai Publication No. S63-227181, memorycapacity is about 5 Mbit. Therefore, a problem inherent in the tableconversion system is that since a large-capacity memory is necessary foreach conversion characteristic, it is difficult to implement the methodby means of an LSI, and it is also impossible to deal with changes inthe condition under which the conversion is carried out.

On the other hand, in the case of the matrix calculation method, forexample, for obtaining printing data of Y, M and C from image data of R,G and B, the following formula (11) is used as a basic calculationformula. $\begin{matrix}{\begin{bmatrix}Y \\M \\C\end{bmatrix} = {({Aij})\begin{bmatrix}R \\G \\B\end{bmatrix}}} & (11)\end{matrix}$

Here, Aij represents coefficients, with i=1 to 3, and j=1 to 3.

However, by the simple linear calculation of the formula (11), it isimpossible to provide a good conversion characteristic because of anon-linearity of an image-printing or the like.

A method has been proposed for providing a conversion characteristic toimprove the foregoing characteristic. This method is disclosed inJapanese Patent Application Kokoku Publication H2-30226, directed to acolor correction calculation device, and employs a matrix calculationformula (12) below. $\begin{matrix}{\begin{bmatrix}Y \\M \\C\end{bmatrix} = {({Dij})\begin{bmatrix}R \\G \\\begin{matrix}B \\{R*G} \\{G*B} \\{B*R} \\{R*R} \\{G*G} \\{B*B} \\N\end{matrix}\end{bmatrix}}} & (12)\end{matrix}$

Here, N is a constant, i=1 to 3, and j=1 to 10.

In the foregoing formula (12), since image data having a mixture of anachromatic component and a color component is directly used, mutualinterference occur in computation. In other words, if one of thecoefficients is changed, influence is given to the components or huesother than the target component or hue (the component or hue for whichthe coefficient is changed). Consequently, a good conversioncharacteristic cannot be realized.

A color conversion method disclosed in Japanese Patent Application KokaiPublication H7-170404 is a proposed solution to this problem. FIG. 20 isa block circuit diagram showing the color conversion method forconversion of image data of R, G and B into printing data of C, M and Y,disclosed in Japanese Patent Application Kokai Publication H7-170404. Inthe drawing, reference numeral 100 denotes a complement calculator; 101,a minimum and maximum calculator; 102, a hue data calculator; 103, apolynomial calculator; 104, a matrix calculator; 105, a coefficientgenerator; and 106, a synthesizer.

Next, the operation will be described. The complement calculator 100receives image data R, G and B, and outputs complementary color data Ci,Mi and Yi which have been obtained by determining 1's complements.

The determination of 1's complement of an input data can be achieved bysubtracting the value of the input data of n bits (n being an integer)from (2^(n)−1). For example, in the case of 8-bit data, the value of theinput data is deducted from “255”.

The minimum and maximum calculator 101 outputs a maximum value β and aminimum value α of this complementary color data and an identificationcode S for indicating, among the six hue data, data which are zero.

The hue data calculator 102 receives the complementary color data Ci, Miand Yi and the maximum and minimum values β and α, and outputs six huedata r, g, b, y, m and c which are obtained by executing the followingsubtraction:

-   -   r=β−Ci,    -   g=β−Mi,    -   b=β−Yi,    -   y=Yi−α,    -   m=Mi−α, and    -   c=Ci−α.        Here, among the six hue data, at least two assume the value        zero.

The polynomial calculator 103 receives the hue data and theidentification code S, selects, from r, g and b, two data Q1 and Q2which are not zero and, from y, m and c, two data P1 and P2 which arenot zero. Based on these data, the polynomial calculator 103 computespolynomial data:

-   -   T1=P1*P2,    -   T3=Q1*Q2,    -   T2=T1/(P1+P2), and    -   T4=T3/(Q1+Q2),        and then outputs the results of the calculation.

It is noted that asterisks “*” are sometimes used in this specificationto indicate multiplication.

The coefficient generator 105 generates calculation coefficients U(Fij)and fixed coefficients U(Eij) for the polynomial data based oninformation of the identification code S. The matrix calculator 104receives the hue data y, m and c, the polynomial data T1 to T4 and thecoefficients U, and outputs the result of the following formula (13) ascolor ink data C1, M1 and Y1. $\begin{matrix}{\begin{bmatrix}{C1} \\{M1} \\{Y1}\end{bmatrix} = {{({Eij})\begin{bmatrix}c \\m \\y\end{bmatrix}} + {({Fij})\begin{bmatrix}{c*m} \\{m*y} \\{y*c} \\{r*g} \\{g*b} \\\begin{matrix}{b*r} \\{c*{m/( {c + m} )}} \\{m*{y/( {m + y} )}} \\{y*{c/( {y + c} )}} \\{r*{g/( {r + g} )}} \\{g*{b/( {g + b} )}} \\{b*{r/( {b + r} )}}\end{matrix}\end{bmatrix}}}} & (13)\end{matrix}$

The synthesizer 106 adds together the color ink data C1, M1 and Y1 anddata α which is the achromatic data, and outputs printing data C, M andY. Accordingly, the following formula (14) is used for obtainingprinting data. $\begin{matrix}{\begin{bmatrix}C \\M \\Y\end{bmatrix} = {{({Eij})\begin{bmatrix}c \\m \\y\end{bmatrix}} + {({Fij})\begin{bmatrix}{c*m} \\{m*y} \\{y*c} \\{r*g} \\{g*b} \\\begin{matrix}{b*r} \\{c*{m/( {c + m} )}} \\{m*{y/( {m + y} )}} \\{y*{c/( {y + c} )}} \\{r*{g/( {r + g} )}} \\{g*{b/( {g + b} )}} \\{b*{r/( {b + r} )}}\end{matrix}\end{bmatrix}} + \begin{bmatrix}\alpha \\\alpha \\\alpha\end{bmatrix}}} & (14)\end{matrix}$

The formula (14) shows a general formula for a group of pixels.

FIG. 21A to FIG. 21F, which are schematic diagrams, show relationsbetween six hues of red (R), green (G), blue (B), yellow (Y), cyan (C)and magenta (M), and hue data y, m, c, r, g and b. As shown, each huedata relates to three hues (i.e., extends over the range of three hues).For instance the hue data c relates to the hues g, c and b.

FIG. 22A to FIG. 22F, which are schematic diagrams, show relationsbetween the six hues and product terms y*m, r*g, c*y, g*b, m*c and b*r.

As shown, each of the six product terms y*m, m*c, c*y, r*g, g*b and b*rin the formula (14) relates to only one hue among the six hues of red,blue, green, yellow, cyan and magenta. That is, only y*m is an effectiveproduct term for red; m*c for blue; c*y for green; r*g for yellow; g*bfor cyan; and b*r for magenta.

Also, each of the six fraction terms y*m/(y+m), m*c/(m+c), c*y/(c+y),r*g/(r+g), g*b/(g+b) and b*r/(b+r) in the formula (14) relates to onlyone hue among the six hues.

As apparent from the foregoing, according to the color conversion methodshown in FIG. 20, by changing coefficients for the product terms and thefraction terms regarding the specific hue, only the target hue can beadjusted without influencing other hues.

Each of the foregoing product terms is determined by a second-ordercomputation for chroma, and each of the fraction terms is determined bya first-order computation for chroma. Thus, by using both of the productterms and the fraction terms, the non-linearity of an image-printing forchroma can be adjusted.

However, this color conversion method cannot satisfy a certain desire.That is, depending on the user's preference, if an area in a color spaceoccupied by specific hues is to be expanded or reduced, e.g.,specifically, if expansion or reduction in an area of red in a colorspace including magenta, red and yellow is desired, the conventionalcolor conversion method of the matrix computation type could not meetsuch a desire.

The problems of the conventional color conversion method or colorconversion device are summarized as follows. Where the color conversiondevice is of a three-dimensional look-up table conversion methodemploying a memory such as ROM, a large-capacity memory is required, anda conversion characteristic cannot be flexibly changed. Where the colorconversion device is of a type using a matrix calculation method,although it is possible to change only a target hue, it is not possibleto vary the color in the inter-hue areas between adjacent ones of thesix hues of red, blue, green, yellow, cyan and magenta, and goodconversion characteristics cannot be realized throughout the entirecolor space.

SUMMARY OF THE INVENTION

The present invention was made to solve the foregoing problems.

An object of the present invention is to provide a color conversiondevice and a color conversion method for performing color-conversionwherein independent adjustment is performed not only for six hues ofred, blue, green, yellow, cyan and magenta but also six inter-hue areasof red-yellow, yellow-green, green-cyan, cyan-blue, blue-magenta andmagenta-red, and a conversion characteristic can be flexibly changed,and no large-capacity memories, such as three-dimensional look-uptables, are necessary.

According to a first aspect of the invention, there is provided a colorconversion device for performing pixel-by-pixel color conversion from afirst set of three color data representing red, green and blue, or cyan,magenta and yellow, into a second set of three color data representingred, green and blue, or cyan, magenta, and yellow, said devicecomprising:

-   -   first calculation means for calculating a minimum value α and a        maximum value β of said first set of three color data for each        pixel;    -   hue data calculating means for calculating hue data r, g, b, y,        m and c based on said first set of three color data, and said        minimum and maximum values α and β outputted from said        calculating means;    -   means for generating first comparison-result data based on the        hue data outputted from said hue data calculating means;    -   means for generating second comparison-result data based on said        first comparison-result data;    -   second calculation means for performing calculation using the        hue data outputted from said hue data calculating means to        produce calculation result data;    -   coefficient storage means for storing matrix coefficients for        the hue data, the calculation result data, the first        comparison-result data and the second comparison-result data;    -   coefficient setting means for setting specified matrix        coefficients in said coefficient storage means; and    -   third calculation means responsive to said hue data, said first        comparison-result data, said second comparison-result data, said        calculation result data, and the coefficients from said        coefficient storage means for calculating said second set of        three color data representing red, green and blue, or cyan,        magenta, and yellow,    -   said first calculation means performing calculation including        matrix calculation performed at least on said hue data, said        first comparison-result data, said second comparison-result        data, said calculation result data, and the coefficients from        said coefficient storage means.

With the above arrangement, it is possible to independently vary notonly the colors of the six hues of red, blue, green, yellow, cyan andmagenta, the colors in the six inter-hue areas of red-yellow,yellow-green, green-cyan, cyan-blue, blue-magenta, and magenta-red, byindependently setting the coefficients relating to the target hue orinter-hue area. Accordingly, it is possible to obtain color conversionmethods or color conversion devices which can change the conversioncharacteristics flexibly, without requiring a large-capacity memory.

Moreover, by making it possible to set the coefficients by the use ofthe coefficient setting means, it is possible to obtain colorreproducibility taking into consideration the characteristics of theoutput device or the input device with which the color conversion deviceof the invention is to be used or the color conversion characteristicspreferred by the user. The coefficients can be set freely by the user,so as to alter the color reproducibility. This is a significantadvantage because different users prefer different colorreproducibilities.

The color reproducibility can also be altered when a three-dimensionallook-up table is used as in the prior art. However, because a largeamount of data, e.g., 5 Mbit, needs to be set, the setting requiresconsiderable time. For instance, if the clock-frequency is 5 MHz, andthe data is set using a three-wire serial interface, at least about onesecond is required. In contrast, according to the invention, the amountof data that needs to be set is several hundred bits. The time requiredfor the setting is at most about 100 microseconds.

A real-time man-machine interface can be therefore achieved, in whichthe color conversion characteristics are changed a little by little, andthe result of the change is observed, until a desired characteristicsare obtained.

In the process of manufacturing the display device for displaying thecolor image, by providing the color conversion device according to theinvention in order to absorb the manufacturing variations in the colorreproducibility of a liquid crystal display panel of a liquid crystaldisplay device, it is possible to set the coefficients necessary tocompensate for the manufacturing variations in a coefficient storage,e.g., a read-only memory, in a short time.

Accordingly, the color conversion device according to the invention isappropriate from the view-point of mass production.

Moreover, because the second comparison-result data calculated from thefirst comparison-result data are used as calculation term relating tothe inter-hue areas in the matrix calculation, the number of calculationsteps required can be reduced than if they are calculated from the huedata r, g, b, y, m, c.

It may be so configured that said third calculation means performs saidmatrix calculation on said hue data, said first comparison-result data,said second comparison-result data, said calculation result data, andthe coefficients from said coefficient storage means, and furtherincludes synthesizing means for adding said minimum value α from saidfirst calculation means to the results of said matrix calculation.

It may be so configured that

-   -   said coefficient storage means outputs predetermined matrix        coefficients Eij (i=1 to 3, J=1 to 3), and Fij (i=1 to 3, j=1 to        18), and    -   said third calculation means performs the calculation using the        hue data, said said first comparison-result data, said second        comparison-result data, said calculation result data, said        minimum value α from said calculating means, and said matrix        coefficients to determine said second set of three color data        representing red, green and blue, denoted by Ro, Go and Bo, in        accordance with the following formula (1): $\begin{matrix}        {\begin{bmatrix}        {Ro} \\        {Go} \\        {Bo}        \end{bmatrix} = {{({Eij})\begin{bmatrix}        r \\        g \\        b        \end{bmatrix}} + {({Fij})\begin{bmatrix}        {c*m} \\        {m*y} \\        {y*c} \\        {r*g} \\        {g*b} \\        {b*r} \\        {h1r} \\        {h1g} \\        {h1b} \\        {h1c} \\        {h1m} \\        {h1y} \\        {h2ry} \\        {h2rm} \\        {h2gy} \\        {h2gc} \\        {h2bm} \\        {h2bc}        \end{bmatrix}} + \begin{bmatrix}        \alpha \\        \alpha \\        \alpha        \end{bmatrix}}} & (1)        \end{matrix}$        wherein h1 r, h1 g, h1 b, h1 c, h1 m and h1 y denote said first        comparison-result data, and h2 ry, h2 rm, h2 gy, h2 gc, h2 bm        and h2 bc denote said second comparison result data.

It may be so configured that

-   -   said coefficient storage means outputs predetermined matrix        coefficients Eij (i=1 to 3, J=1 to 3), and FiJ (i=1 to 3, J=1 to        18), and    -   said third calculation means performs the calculation using the        hue data, said said first comparison-result data, said second        comparison-result data, said calculation result data, said        minimum value a from said calculating means, and said matrix        coefficients to determine said second set of three color data        representing cyan, magenta and yellow denoted by Co, Mo and Yo,        in accordance with the following formula (2): $\begin{matrix}        {\begin{bmatrix}        {Co} \\        {Mo} \\        {Yo}        \end{bmatrix} = {{({Eij})\begin{bmatrix}        c \\        m \\        y        \end{bmatrix}} + {({Fij})\begin{bmatrix}        {c*m} \\        {m*y} \\        {y*c} \\        {r*g} \\        {g*b} \\        {b*r} \\        {h1r} \\        {h1g} \\        {h1b} \\        {h1c} \\        {h1m} \\        {h1y} \\        {h2ry} \\        {h2rm} \\        {h2gy} \\        {h2gc} \\        {h2bm} \\        {h2bc}        \end{bmatrix}} + \begin{bmatrix}        \alpha \\        \alpha \\        \alpha        \end{bmatrix}}} & (2)        \end{matrix}$        wherein h1 r, h1 g, h1 b, h1 c, h1 m and h1 y denote said first        comparison-result data, and h2 ry, h2 rm, h2 gy, h2 gc, h2 bm        and h2 bc denote said second comparison result data.

It may be so configured that said third calculation means performs saidmatrix calculation on said hue data, said first comparison-result data,said second comparison-result data, said calculation result data, thecoefficients from said coefficient storage means, and said minimum valueα from said first calculation means.

It may be so configured that

-   -   said coefficient storage means outputs predetermined matrix        coefficients Eij (i=1 to 3, J=1 to 3), and Fij (i=1 to 3, J=1 to        19), and    -   said third calculation means performs the calculation using the        hue data, said said first comparison-result data, said second        comparison-result data, said calculation result data, said        minimum value α from said calculating means, and said matrix        coefficients to determine said second set of three color data        representing red, green and blue, denoted by Ro, Go and Bo, in        accordance with the following formula (3): $\begin{matrix}        {\begin{bmatrix}        {Ro} \\        {Go} \\        {Bo}        \end{bmatrix} = {{({Eij})\begin{bmatrix}        r \\        g \\        b        \end{bmatrix}} + {({Fij})\begin{bmatrix}        {c*m} \\        {m*y} \\        {y*c} \\        {r*g} \\        {g*b} \\        {b*r} \\        {h1r} \\        {h1g} \\        {h1b} \\        {h1c} \\        {h1m} \\        {h1y} \\        {h2ry} \\        {h2rm} \\        {h2gy} \\        {h2gc} \\        {h2bm} \\        {h2bc} \\        \alpha        \end{bmatrix}}}} & (3)        \end{matrix}$        wherein h1 r, h1 g, h1 b, h1 c, h1 m and h1 y denote said first        comparison-result data, and h2 ry, h2 rm, h2 gy, h2 gc, h2 bm        and h2 bc denote said second comparison result data.

It may be so configured that

-   -   said coefficient storage means outputs predetermined matrix        coefficients Eli (i=1 to 3, j=1 to 3), and Fij (i=1 to 3, J=1 to        19), and    -   said third calculation means performs the calculation using the        hue data, said said first comparison-result data, said second        comparison-result data, said calculation result data, said        minimum value α from said calculating means, and said matrix        coefficients to determine said second set of three color data        representing cyan, magenta and yellow denoted by Co, Mo and Yo,        in accordance with the following formula (4): $\begin{matrix}        {\begin{bmatrix}        {Co} \\        {Mo} \\        {Yo}        \end{bmatrix} = {{({Eij})\begin{bmatrix}        c \\        m \\        y        \end{bmatrix}} + {({Fij})\begin{bmatrix}        {c*m} \\        {m*y} \\        {y*c} \\        {r*g} \\        {g*b} \\        {b*r} \\        {h1r} \\        {h1g} \\        {h1b} \\        {h1c} \\        {h1m} \\        {h1y} \\        {h2ry} \\        {h2rm} \\        {h2gy} \\        {h2gc} \\        {h2bm} \\        {h2bc} \\        \alpha        \end{bmatrix}}}} & (4)        \end{matrix}$        wherein h1 r, h1 g, h1 b, h1 c, h1 m and h1 y denote said first        comparison-result data, and h2 ry, h2 rm, h2 gy, h2 gc, h2 bm        and h2 bc denote said second comparison result data.

It may be so configured that

-   -   said first set of three color data represent red, green and        blue,    -   said second set of three color data represent red, green and        blue, and    -   said hue data calculation means calculates the hue data r, g, b,        y, m, c by subtraction in accordance with:    -   r=Ri−α,    -   g=Gi−α,    -   b=Bi−α,    -   y=β−Bi,    -   m=β−Gi, and    -   c=β−Ri,        wherein Ri, Gi and Bi represent said first set of three color        data.

It may be so configured that

-   -   said first set of three color data represent cyan, magenta and        yellow,    -   said second set of three color data represent red, green and        blue,    -   said device further comprises means for determining complement        of said first set of three color data, and    -   said hue data calculation means calculates the hue data r, g, b,        y, m, c by subtraction in accordance with:    -   r=Ri−α,    -   g=Gi−α,    -   b=Bi−α,    -   y=β−Bi,    -   m=β−Gi, and    -   c=β−Ri,        wherein Ri, Gi and Bi represent data produced by the        determination of the complement of said first set of three color        data.

It may be so configured that

-   -   said first set of three color data represent cyan, magenta and        yellow,    -   said second set of three color data represent cyan, magenta and        yellow, and    -   said hue data calculation means calculates the hue data r, g, b,        y, m, c by subtraction in accordance with:    -   r=−Ci,    -   g=β−Mi,    -   b=β−Yi,    -   y=Yi−α,    -   m=Mi−α, and    -   c=Ci−α,        wherein Ci, Mi and Yi represent said first set of three color        data.

It may be so configured that

-   -   said first set of three color data represent red, green and        blue,    -   said second set of three color data represent cyan, magenta and        yellow,    -   said device further comprises means for determining complement        of said first set of three color data, and    -   said hue data calculation means calculates the hue data r, g, b,        y, m, c by subtraction in accordance with:    -   r=β−Ci,    -   g=β−Mi,    -   b=β−Yi,    -   y=Yi−α,    -   m=Mi−α, and    -   c=Ci−α,        wherein Ci, Mi and Yi represent data produced by the        determination of the complement of said first set of three color        data.

With the above arrangement, the hue data calculating means can beconfigured of means for performing subtraction based on the input imageof red, green and blue, or cyan, magenta and yellow and the maximumvalue β and minimum value α from the first calculation means.

It may be so configured that

-   -   said first comparison-result data generating means determines        the comparison-result data among the hue data r, g and b, and        the comparison-result data among the hue data y, m and c, and    -   said second comparison-result data generating means comprises        multiplying means for multiplying the first comparison-result        data outputted from said first comparison-result data generating        means with specific calculation coefficients, and means for        determining the comparison-result data based on the outputs of        said multiplication means.

With the above arrangement, the first comparison-result data generatingmeans and the second comparison-result data generating means areconfigured of means for performing comparison, and means for performingmultiplication.

It may be so configured that

-   -   said first comparison-result data generating means determines        the first comparison-result data:    -   h1 r=min (m, y),    -   h1 g=min (y, c),    -   h1 b=min (c, m),    -   h1 c=min (g, b),    -   h1 m=min (b, r), and    -   h1 y=min (r, g),        (with min (A, B) representing the minimum value of A and B),    -   said second comparison-result data generating means determines        the second comparison-result data:    -   h2 ry=min (aq1*h1 y, ap1*h1 r),    -   h2 rm=min (aq2*h1 m, ap2*h1 r),    -   h2 gy=min (aq3*h1 y, ap3*h1 g),    -   h2 gc=min (aq4*h1 c, ap4*h1 g),    -   h2 bm=min (aq5*h1 m, ap5*h1 b), and    -   h2 bc=min (aq6*h1 c, ap6*h1 m).

With the above arrangement, the first comparison-result data generatingmeans can be configured of means for performing minimum value selection,and the second comparison-result data can be configured of means forperforming multiplication and means for performing minimum valueselection.

It may be so configured that said multiplying means in said secondcomparison-result data generating means performs calculation on saidfirst comparison result-data and said calculation coefficients bysetting said calculation coefficients aq1 to aq6 and ap1 to ap6 tointegral values of 2^(n), with n being an integer, and by bit shifting.

With the above arrangement, the multiplication can be carried out bymeans of bit shifting.

It may be so configured that said second calculation means determinesproducts of the hue data.

With the above arrangement, said second calculation means can beconfigured of means for performing multiplication.

It may be so configured that each of said first comparison-result datais determined from two of the hue data and is effective for only one ofthe six hues of red, green, blue, cyan, magenta and yellow.

With the above arrangement, each of the six hues can be adjusted byvarying the coefficients for the first comparison-result data withoutinfluencing other hues.

It may be so configured that

-   -   each of said second comparison-result data is determined from        two of the first comparison-result data and is effective for        only one of the six inter-hue areas of red-yellow, yellow-green,        green-cyan, cyan-blue, blue-magenta, and magenta-red.

With the above arrangement, each of the six inter-hue areas can beadjusted by varying the coefficients for the second comparison-resultdata without influencing other inter-hue areas.

It may be so configured that

-   -   said coefficient storage means outputs specified matrix        coefficients Eij (i=1 to 3, j=1 to 3) based on a formula (5)        below: $\begin{matrix}        {({Eij}) = \begin{bmatrix}        1 & 0 & 0 \\        0 & 1 & 0 \\        0 & 0 & 1        \end{bmatrix}} & (5)        \end{matrix}$        and generates the matrix coefficients Fij (i=1 to 3, j=1 to 18,        or J=1 to 19) such that, of the coefficients Fij, the        coefficients for said calculation result data are set to zero,        and other coefficients are set to specified values.

With the above arrangement, it is not necessary to calculate the productterms for which the coefficients are zero, and yet it is possible tolinearly adjust only the target hue or inter-hue areas (among the sixhues of hues of red, blue, green yellow, cyan, and magenta, and the sixinter-hue area) without influencing other hues and inter-hue areas.

It may be so configured that

-   -   said first calculation means calculates a maximum value β and a        minimum value α using said first set of three color data, and        generates an identification code indicating the hue data which        is of a value zero, and    -   said second calculation means performs arithmetic operation on        said hue data based on the identification code outputted from        said first calculation means,    -   said coefficient storage means outputs said matrix coefficients        based on the identification code outputted from said first        calculation means, and    -   said third calculation means performs matrix calculation using        the coefficient from said coefficient storage means to produce        the second set of three color data based on the identification        code outputted from said first calculation means.

With the above arrangement, the number of steps of second calculationmeans for performing the matrix calculation can be reduced.

According to another aspect of the invention, there is provided a methodof manufacturing a color conversion device which is for use with aninput or output device and which performs pixel-by-pixel colorconversion from a first set of three color data representing red, greenand blue, or cyan, magenta and yellow, into a second set of three colordata representing red, green and blue, or cyan, magenta, and yellow,said color conversion device comprising:

-   -   first calculation means for calculating a minimum value α and a        maximum value β of said first set of three color data for each        pixel;    -   hue data calculating means for calculating hue data r, g, b, y,        m and c based on said first set of three color data, and said        minimum and maximum values α and β outputted from said        calculating means;    -   means for generating first comparison-result data based on the        hue data outputted from said hue data calculating means;    -   means for generating second comparison-result data based on said        first comparison-result data;    -   second calculation means for performing calculation using the        hue data outputted from said hue data calculating means to        produce calculation result data;    -   coefficient storage means for storing coefficients for the hue        data, the calculation result data, the first comparison-result        data and the second comparison-result data; and    -   third calculation means responsive to said hue data, said first        comparison-result data, said second comparison-result data, said        calculation result data, and the coefficients from said        coefficient storage means for calculating said second set of        three color data representing red, green and blue, or cyan,        magenta, and yellow, said means performing calculation including        matrix calculation performed at least on said hue data, said        first comparison-result data, said second comparison-result        data, said calculation result data, and the coefficients from        said coefficient storage means, said method comprising the steps        of:    -   (a) producing a device which includes the above-recited        elements, but in which said coefficients are not stored in said        storage means; and    -   (b) writing said coefficients in said coefficient storage taking        into consideration the characteristics of the device with which        the color conversion device is to be used.

BRIEF DESCRIPTION OF THE DRAWINGS

In the accompanying drawings:—

FIG. 1 is a block diagram showing an example of configuration of a colorconversion device of Embodiment 1 of the present invention;

FIG. 2 is a block diagram showing an example of configuration of apolynomial calculator included in the color conversion device ofEmbodiment 1;

FIG. 3 is a table showing an example of the relationship between anidentification code S1, and the maximum and minimum values β and α, andhue data whose value is zero, in the color conversion device ofEmbodiment 1;

FIG. 4 is a table showing the operation of a zero remover of thepolynomial calculator in the color conversion device of Embodiment 1;

FIG. 5 is a block diagram showing an example of configuration of amatrix calculator included in the color conversion device of Embodiment1;

FIG. 6A to FIG. 6F are diagrams schematically showing the relationshipbetween six six hues and hue data;

FIG. 7A to FIG. 7F are diagrams schematically showing the relationshipbetween six hues and product terms in the color conversion device ofEmbodiment 1;

FIG. 8A to FIG. 8F are diagrams schematically showing the relationshipbetween six hues and first comparison-result data in the colorconversion device of Embodiment 1;

FIG. 9A to FIG. 9F are diagrams schematically showing the relationshipbetween six inter-hue areas and second comparison-result data in thecolor conversion device of Embodiment 1;

FIG. 10A to FIG. 10F are diagrams schematically showing how the range ofeach inter-hue area is changed with the change of the coefficientsmultiplied at the polynomial calculator is changed;

FIG. 11A and FIG. 11B are tables showing the relationship betweenrespective hues or inter-hue areas, and effective calculation terms ordata which relate to and are effective for each hue or inter-hue area;

FIG. 12 is an xy chromaticity diagram illustrating the gamut of thecolor reproduction of the input color signals and the gamut of a desiredcolor reproduction, for explaining the operation of Embodiment 1;

FIG. 13 is an xy chromaticity diagram illustrating the gamut of thecolor reproduction obtained by adjusting the coefficients for the firstcomparison-result data, together with the gamut of the desired colorreproduction, for explaining the operation of Embodiment 1;

FIG. 14 is an xy chromaticity diagram for explaining the gamut of thecolor reproduction obtained by adjusting the coefficients for the firstand second comparison-result data, together with the gamut of thedesired color reproduction, for explaining the operation of Embodiment1;

FIG. 15 is a block diagram showing an example of configuration of acolor conversion device of Embodiment 2 of the present invention;

FIG. 16 is a block diagram showing an example of configuration ofEmbodiment 3 of the present invention;

FIG. 17 is a block diagram showing part of an example of configurationof a matrix calculator included in the color conversion device ofEmbodiment 3;

FIG. 18 is a block diagram showing an example of configuration of acolor conversion device of Embodiment 4 of the present invention;

FIG. 19 is a block diagram showing an example of configuration of acolor conversion device of Embodiment 5 of the present invention;

FIG. 20 is a block diagram showing an example of configuration of aconventional color conversion device;

FIG. 21A to FIG. 21F are diagrams schematically showing the relationshipbetween six hues and hue data in the conventional color conversiondevice; and

FIG. 22A to FIG. 22F are diagrams schematically showing the relationshipbetween six hues and calculation terms in a matrix calculator includedin the conventional color conversion device.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Next, the preferred embodiments of the present invention will bedescribed in detail with reference to the accompanying drawings.

Embodiment 1

FIG. 1 is a block diagram showing an example of configuration of a colorconversion device of Embodiment 1 of the present invention. Theillustrated color conversion device is for converting a first set ofthree color data representing red, green and blue, denoted by Ri, Gi andBi, into a second set of three color data, also representing red, greenand blue, denoted by Ro, Go and Bo. A minimum and maximum calculator 1calculates a maximum value β and a minimum value α of the inputted imagedata denoted by Ri, Gi and Bi, and generates and outputs anidentification code S1 for indicating, among the six hue data, datawhich are zero, as will be better understood from the followingdescription. A hue data calculator 2 calculates hue data r, g, b, y, mand c from the image data Ri, Gi and Bi and the outputs from the minimumand maximum calculator 1. The color conversion device further comprisesa polynomial calculator 3, a matrix calculator 4, a coefficient storage5, a synthesizer 6, and a coefficient setting unit 15, which will bedescribed later.

The coefficient setting unit 15 is manipulated by a human operator tofreely set the coefficients. It may comprise a combination of akeyboard, a display unit, and a control unit for controlling the displayunit, and receiving and processing commands and/or data input by the useof the keyboard.

FIG. 2 is a block diagram showing an example of configuration of thepolynomial calculator 3. In FIG. 2, a zero remover 7 removes, from theinputted hue data, data which are of value zero. Reference numerals 8 aand 8 b denote multipliers. Minimum selectors 9 a, 9 b and 9 c selectand output the minimum of the input data. A calculation coefficientselector 11 selects from among the coefficients stored in thecoefficient storage 5, and outputs the selected coefficients ascalculation coefficients based on the identification code S1 from theminimum and maximum calculator 1. The selector may comprise a memorycontroller, which may be a CPU operating under a control program storedin a program memory, not shown as such. The selector supplies an addresssignal AD to the coefficient storage 5 to read the data representing thecoefficients stored at the memory location designated by the address.

Arithmetic units 10 a and 10 b perform multiplication between thecalculation coefficients represented by the outputs of the calculationcoefficient selector 11 and the outputs from the minimum selectors 9 aand 9 b.

Next, the operation will be described. The inputted image data Ri, Giand Bi corresponding to the three colors of red, green and blue are sentto the minimum and maximum calculator 1 and the hue data calculator 2.The minimum and maximum calculator 1 calculates and outputs a maximumvalue β and a minimum value α of the inputted image data Ri, Gi and Bi,and also generates and outputs an identification code S1 for indicating,among the six hue data, data data which are zero.

The hue data calculator 2 receives the inputted image data Ri, Gi and Biand the maximum and minimum values β and α from the minimum and maximumcalculator 1, performs subtraction of

-   -   r=Ri−α,    -   g=Gi−α,    -   b=Bi−α,    -   y=β−Bi,    -   m=β−Gi and    -   c=β−Ri,        and outputs six hue data r, g, b, y, m and c thus obtained.

The maximum and minimum values β and α calculated by the minimum andmaximum calculator 1 are respectively represented as follows:

-   -   β=MAX (Ri, Gi, Bi)    -   α=MIN (Ri, Gi, Bi)        Since the six hue data r, g, b, y, m and c calculated by the hue        data calculator 2 are obtained by the subtraction of    -   r=Ri−α,    -   g=Gi−α,    -   b=Bi−α,    -   y=β−Bi,    -   m=β−Gi and    -   c=β−Ri,        at least two among these six hue data are of a value zero. For        example, if a maximum value β is Ri and a minimum value α is Gi        (β=Ri, and α=Gi), g=0 and c=0. If a maximum value β is Ri and a        minimum value α is Bi (β=Ri, and α=Bi), b=0 and c=0. In other        words, in accordance with a combination of Ri, Gi and Bi which        are the largest and the smallest, respectively, one of r, g and        b, and one of y, m and c, i.e., in total two of them have a        value zero.

Thus, in the foregoing minimum and maximum calculator 1, theidentification code S1 for indicating, among the six hue data which arezero are generated and outputted. The identification code S1 can assumeone of the six values, depending on which of Ri, Gi and Bi are of themaximum and minimum values β and α. FIG. 3 shows a relationship betweenthe values of the identification code S1 and the maximum and minimumvalues β and α of Ri, Gi and Bi and hue data which has a value zero. Inthe drawing, the values of the identification code S1 represent just anexample, and the values may be other than those shown in the drawing.

Then, the six hue data r, g, b, y, m and c outputted from the hue datacalculator 2 are sent to the polynomial calculator 3, and the hue datar, g and b are also sent to the matrix calculator 4. The polynomialcalculator 3 also receives the identification code S1 outputted from theminimum and maximum calculator 1, and performs calculation by selecting,from the hue data r, g and b, two data Q1 and Q2 which are not of avalue zero, and from the hue data y, m and c, two data P1 and P2 whichare not of a value zero. Next, this operation will be described byreferring to FIG. 2.

The hue data from the hue data calculator 2 and the identification codeS1 from the minimum and maximum calculator 1 are inputted to the zeroremover 7 in the polynomial calculator 3. The zero remover 7 outputs,based on the identification code S1, the two data Q1 and Q2 which arenot of a value zero, among the hue data r, g and b and the two data P1and P2 which are not of a value zero, among the hue data y, m and c. Forinstance, Q1, Q2, P1 and P2 are determined as shown in FIG. 4, and thenoutputted. If, for example, the identification code S1 is of a valuezero, Q1 and Q2 are obtained from the hue data r and b, and P1 and P2are obtained from the hue data y and m, so the outputs are given byQ1=r, Q2=b, P1=m and P2=y. As in the case of FIG. 3, the values of theidentification code S1 in FIG. 4 represent just an example, and may beother than those shown in FIG. 4.

The data Q1 and Q2 outputted from the zero remover 7 are inputted to themultiplier 8 a, which calculates and outputs the product T3=Q1*Q2. Thedata P1 and P2 outputted from the zero remover 7 are inputted to themultiplier 8 b, which calculates and outputs the product T1=P1*P2.

The minimum selector 9 a selects and outputs the minimum value T4=min(Q1, Q2) among the output data Q1 and Q2 from the zero remover 7. Theminimum selector 9 b selects and outputs the minimum value T2=min (P1,P2) among the output data P1 and P2 from the zero remover 7. The outputsof the minimum selectors 9 a and 9 b are the first comparison-resultdata.

The identification code S1 is inputted from the minimum and maximumcalculator 1 to the calculation coefficient selector 11, which selectssignals indicating calculation coefficients aq and ap from among thesignals stored in the coefficient storage 5, the selection being madebased on the identification code S1, and the coefficient aq is suppliedto the arithmetic unit 10 a, and the coefficient ap is supplied to thearithmetic unit 10 b. These calculation coefficients aq and ap are usedfor multiplication with the comparison-result data T4 and T2, and eachof the calculation coefficients aq and ap can assume one of the sixvalues, corresponding to the value of the identification code S1 shownin FIG. 4. The arithmetic unit 10 a receives the comparison-result dataT4 from the minimum selector 9 a, performs multiplication of aq*T4, andsends the result to the minimum selector 9 c. The arithmetic unit 10 breceives the comparison-result data T2 from the minimum selector 7,performs multiplication of ap*T2, and sends the result to the minimumselector 9 c.

The minimum selector 9 c selects and outputs the minimum value T5=min(aq*T2, ap*T4) of the outputs the arithmetic units 10 a and 10 b. Theoutput of the minimum value selector 9 c is a second comparison-resultdata.

The polynomial data T1, T2, T3, T4 and T5 outputted from the polynomialcalculator 3 are supplied to the matrix calculator 4.

The calculation coefficients U (Fij) and fixed coefficients U (Eij) forthe polynomial data are read or outputted from the coefficient storage 5shown in FIG. 1 based on the identification code S1, and sent to thematrix calculator 4.

The matrix calculator 4 receives the hue data r, g and b from the huedata calculator 2, the polynomial data T1 to T5 from the polynomialcalculator 3 and the coefficients. U from the coefficient storage 5, andoutputs the results of calculation according to the following formula(6) as image data R1, G1 and B1. $\begin{matrix}{\begin{bmatrix}{R1} \\{G1} \\{B1}\end{bmatrix} = {{({Eij})\begin{bmatrix}r \\g \\b\end{bmatrix}} + {({Fij})\begin{bmatrix}{T1} \\{T2} \\{T3} \\{T4} \\{T5}\end{bmatrix}}}} & (6)\end{matrix}$

For (Eij), i=1 to 3 and j=1 to 3, and for (Fij), i=1 to 3 and J=1 to 5.

FIG. 5, which is a block diagram, shows an example of configuration ofpart of the matrix calculator 4. Specifically, it shows how R1 iscalculated and outputted. As shown in FIG. 5, the matrix calculator 4includes multipliers 12 a to 12 f, and adders 13 a to 13 einterconnected as illustrated.

Next, the operation of the matrix calculator 4 of FIG. 5 will bedescribed. The multipliers 12 a to 12 f receive the hue data r, thepolynomial data T1 to T5 from the polynomial calculator 3 and thecoefficients U (Eij) and U (Fij) from the coefficient storage 5, andthen output the products thereof. The adders 13 a and 13 b receive theproducts outputted from the multipliers 12 b to 12 e, add the inputteddata and output the sums thereof. The adder 13 c adds the data from theadders 13 a and 13 b, and the adder 13 d adds the output from the adder13 c and the product outputted from the multiplier 12 f. The adder 13 eadds the output from the adder 13 d and the output from the multiplier12 a, and outputs the sum total thereof as image data R1. In the exampleof configuration shown in FIG. 5, if the hue data r is replaced by thehue data g or b, and coefficients suitable for the respective terms(data) T1 to T5 are used in substitution, image data G1 or B1 can becalculated.

Where it is desired to increase the calculation speed of the colorconversion method or the color conversion device of this embodiment,since parts of the coefficients (Eij) and (Fij) which respectivelycorrespond to the hue data r, g and b are used, the configurations eachas shown in FIG. 5 may be used in parallel, so as to perform the matrixcalculation at a higher speed.

The synthesizer 6 receives the image data R1, G1 and B1 from the matrixcalculator 4 and the minimum value a outputted from the minimum andmaximum calculator 1 representing the achromatic data, performsaddition, and outputs image data Ro, Go and Bo. The equation used forobtaining the image data color-converted by the color-conversion methodof FIG. 1 is therefore given by the following formula (1).$\begin{matrix}{\begin{bmatrix}{Ro} \\{Go} \\{Bo}\end{bmatrix} = {{({Eij})\begin{bmatrix}r \\g \\b\end{bmatrix}} + {({Fij})\begin{bmatrix}{c*m} \\{m*y} \\{y*c} \\{r*g} \\{g*b} \\{b*r} \\{h1r} \\{h1g} \\{h1b} \\{h1c} \\{h1m} \\{h1y} \\{h2ry} \\{h2rm} \\{h2gy} \\{h2gc} \\{h2bm} \\{h2bc}\end{bmatrix}} + \begin{bmatrix}\alpha \\\alpha \\\alpha\end{bmatrix}}} & (1)\end{matrix}$

Here, for (Eij), i=1 to 3 and j=1 to 3, and for (Fij), i=1 to 3 and j=1to 18, and

-   -   h1 r=min (m, y),    -   h1 g=min (y, c),    -   h1 b=min (c, m),    -   h1 c=min (g, b),    -   h1 m=min (b, r),    -   h1 y=min (r, g),    -   h2 ry=min (aq1*h1 y, ap1*h1 r),    -   h2 rm=min (aq2*h1 m, ap2*h1 r),    -   h2 gy=min (aq3*h1 y, ap3*h1 g),    -   h2 gc=min (aq4*h1 c, ap4*h1 g),    -   h2 bm=min (aq5*h1 m, ap5*h1 b), and    -   h2 bc=min (aq6*h1 c, ap6*h1 b),        and aq1 to aq6 and ap1 to ap6 indicate calculation coefficients        selected by the calculation coefficient selector 11 of FIG. 2.

The difference between the number of calculation terms in the formula(1) and the number of calculation terms in FIG. 1 is that FIG. 1 shows amethod of calculation for each pixel excluding the calculation termswhich are of a value zero, while the formula (1) represents a generalformula for a set of pixels. In other words, eighteen polynomial datafor one pixel of the formula (1) can be reduced to five effective data,and this reduction is achieved by exploiting a characteristic of the huedata.

The combination of effective data is changed according to image data ofthe target pixel. For all image data, all the polynomial data can beeffective.

FIG. 6A to FIG. 6F schematically show relations between the six hues(red, yellow, green, cyan, blue, magenta) and the hue data y, m, c, r, gand b. Each hue data relates to, i.e., extends to cover the range ofthree hues. For example, y as shown in FIG. 6A relates to, or extends tocover three hues of red, yellow and green.

FIG. 7A to FIG. 7F schematically show relations between the six hues andthe product terms y*m, r*g, c*y, g*b, m*c and b*r, and it can beunderstood that each product term is a second-order term for a specifiedhue. For example, if W is a constant, since r=W and g=b=0 hold for red,y=m=W and c=0 are obtained. Accordingly, y*m=W*W is realized, and thisterm is a second-order term. The other five terms are all zero. In otherwords, only y*m is an effective second-order term for red. Similarly,c*y is the only effective term for green; m*c for blue; g*b for cyan;b*r for magenta; and r*g for yellow.

Each of the foregoing formulae (6) and (1) includes a firstcomparison-result data effective only for one hue.

The first comparison-result data are:

-   -   h1 r=min (y, m),    -   h1 y=min (r, g)    -   h1 g=min (c, y),    -   h1 c=min (g, b),    -   h1 b=min (m, c), and    -   h1 m=min (b, r).

FIG. 8A to FIG. 8F schematically show relations between the six hues andfirst comparison-result data h1 r, h1 y, h1 g, h1 c, h1 b, and h1 m. Itis seen that each of the first comparison-result data relates to onlyone specific hue.

The six first comparison-result data has the nature of a first-orderterm. For instance, if W is a constant, for red, r=W, g=b=0, so thaty=m=W, and c=0. As a result, min (y, m)=W has a first-order value. Theother five first comparison-result data are all of a value zero. Thatis, for red, h1 r=min (y, m) alone is the only effective firstcomparison-result data. Similarly, h1 g=min (c, y) is the only effectivefirst comparison-result data for green; h1 b=min (m, c) for blue; h1c=min (g, b) for cyan; h1 m=min (b, r) for magenta; and h1 y=min (r, g)for yellow.

Next, a difference between the first-order and second-order terms willbe described. As described above, for red, if W is a constant, y*m=W*Wis realized, and the other product terms are all zero. Here, since theconstant W indicates the magnitudes of the hue signals y and m, themagnitude of the constant W depends on the color brightness or chroma.With y*m=W*W, the product term y*m is a second-order function forchroma. The other product terms are also second-order functions forchroma regarding the hues to which these terms are effective.Accordingly, influence given by each product term to color reproductionis increased in a second-order manner as chroma is increased. In otherwords, the product term is a second-order term which serves as asecond-order adjustment term for chroma in color reproduction.

On the other hand, for red, if W is a constant, h1 r=min (m, m)=W isrealized, and the other first comparison-result data are all zero. Here,the magnitude of the constant W depends of color brightness or chroma.With h1 r=min (y, m)=W, the comparison-result data h1 r=min (y, m) is afirst-order function for chroma. The other first comparison-result dataare also first-order functions for chroma regarding the hues to whichthese terms are effective. Accordingly, the influence given by eachfirst comparison-result data to color reproduction is a first-orderfunction for chroma. In other words, the first comparison-result data isa first-order term which serves as a first-order adjustment term forchroma in color reproduction.

FIG. 9A to FIG. 9F schematically show relations between the six hues andsecond comparison-result data:

-   -   h2 ry=min (h1 y, h1 r),    -   h2 gy=min (h1 y, h1 g),    -   h2 gc=min (h1 c, h1 g),    -   h2 bc=min (h1 c, h1 b),    -   h2 bm=min (h1 m, h1 b), and    -   h2 rm=min (h1 m, h1 r).

This is the case in which the coefficients aq1 to aq6 and ap1 to ap6 in

-   -   h2 ry=min (aq1*h1 y, ap1*h1 r),    -   h2 rm=min (aq2*h1 m, ap2*h1 r),    -   h2 gy=min (aq3*h1 y, ap3*h1 g),    -   h2 gc min (aq4*h1 c, ap4*h1 g),    -   h2 bm=min (aq5*h1 m, ap5*h1 b), and    -   h2 bc=min (aq6*h1 c, ap6*h1 b),        in the formula (1) above are all of a value “1”.

It can be understood from FIG. 9A to FIG. 9F, that each of the secondcomparison-result data relates to changes in the six inter-hue areas ofred-green, yellow-green, green-cyan, cyan-blue, blue-magenta, andmagenta-red. In other words, for red-yellow, b=c=0, and the five termsother than h2 ry=min (h1 y, h1 r)=min (min (r, g), min (y, m)) are allzero. Accordingly, only h2 ry is an effective second comparison-resultdata for red-yellow. Similarly, only h2 gy is an effective secondcomparison-result data for yellow-green; h2 gc for green-cyan; h2 bc forcyan-blue; h2 bm for blue-magenta; and h2 rm for magenta-red.

Moreover, the range of the inter-hue area to which each of the secondcomparison-result data relates is half that of the range of the hue towhich each of the first comparison-result data relates.

FIG. 10A to FIG. 10F schematically show how the range of the sixinter-hue area to which each of the second comparison-result data relateis changed when the coefficients aq1 to aq6 and ap1 to ap6 used fordetermination of h2 ry, h2 rm, h2 gy, h2 gc, h2 bm and h2 bc accordingto the foregoing formulae (6) and (1) are changed. The broken lines a1to a6 shows the characteristics when aq1 to aq6 assume values largerthan ap1 to ap6. The broken lines b1 to b6 shows the characteristicswhen ap1 to ap6 assume values larger than aq1 to aq6.

Specifically, for inter-hue area red-yellow, only h2 ry=min (aq1*h1 y,ap1*h1 r) is an effective second comparison-result data. If, forexample, the ratio between aq1 and ap1 is 2:1, the peak value of thesecond comparison-result data is shifted toward red, as indicated by thebroken line a1 in FIG. 10A, and thus it can be made an effectivecomparison-result data for an area closer to red in the inter-hue areaof red-yellow. On the other hand, for example if the ratio between aq1and ap1 is 1:2, the relationship is like that indicated by the brokenline b1 in FIG. 10A, the peak value of the second comparison-result datais shifted toward yellow, and thus it can be made an effectivecomparison-result data for an area closer to yellow in the inter-huearea of red-yellow. Similarly, by respectively changing:

-   -   aq3 and ap3 in h2 gy for yellow-green,    -   aq4 and ap4 in h2 gc for green-cyan,    -   aq6 and ap6 in h2 bc for cyan-blue,    -   aq5 and ap5 in h2 bm for blue-magenta and    -   aq2 and ap2 in h2 rm for magenta-red,        in the area for which each second comparison-result data is most        effective can be changed.

FIG. 11A and FIG. 11B respectively show relations between the six huesand inter-hue areas and effective calculation terms. Thus, if thecoefficients which are stored in the coefficient storage 5 and which arefor a calculation term effective for a hue or an inter-hue area to beadjusted are changed, only the target hue or inter-hue area can beadjusted. Further, if coefficients selected by the calculationcoefficient selector 11 in the polynomial calculator 3 are changed, partof the inter-hue area where a calculation term in the inter-hue area ismost effective can be changed without giving any influence to the otherhues.

Next, an example of coefficients outputted from the coefficient storage5 of Embodiment 1 described above with reference to FIG. 1 will bedescribed. The following formula (5) shows an example of coefficients U(Eij) outputted from the coefficient storage 5. $\begin{matrix}{({Eij}) = \begin{bmatrix}1 & 0 & 0 \\0 & 1 & 0 \\0 & 0 & 1\end{bmatrix}} & (5)\end{matrix}$

If the coefficients U (Fij) in the foregoing formula are all zero thisrepresents the case where color conversion is not executed. Thefollowing formula (7) shows the case where, of the coefficients U (Fij),the coefficients for second-order calculation terms which are productterms are all zero, and coefficients for first comparison-result dataand second comparison-result data, both of which are first-ordercalculation terms, are represented by, for example Ar1 to Ar3, Ay1 toAy3, Ag1 to Ag3, Ac1 to Ac3, Ab1 to Ab3, Am1 to Am3, Ary1 to Ary3, Agy1to Agy3, Agc1 to Agc3, Abc1 to Abc3, Abm1 to Abm3 and Arm1 to Arm3.$\begin{matrix}{({Fij}) = \begin{bmatrix}0 & 0 & 0 & 0 & 0 & 0 & {Ar1} & {Ag1} & {Ab1} & {Ac1} & {Am1} & {Ay1} & {Ary1} & {Arm1} & {Agy1} & {Agc1} & {Abm1} & {Abc1} \\0 & 0 & 0 & 0 & 0 & 0 & {Ar2} & {Ag2} & {Ab2} & {Ac2} & {Am2} & {Ay2} & {Ary2} & {Arm2} & {Agy2} & {Agc2} & {Abm2} & {Abc2} \\0 & 0 & 0 & 0 & 0 & 0 & {Ar3} & {Ag3} & {Ab3} & {Ac3} & {Am3} & {Ay3} & {Ary3} & {Arm3} & {Agy3} & {Agc3} & {Abm3} & {Abc3}\end{bmatrix}} & (7)\end{matrix}$

In the foregoing, adjustment is performed by using the firstcomparison-result data and second comparison-result data, both of whichare first-order calculation terms. Accordingly, only a hue or aninter-hue area can be linearly adjusted. If coefficients relating to afirst-order calculation term for a hue or an inter-hue area to beadjusted are set to values other than zero, and the other coefficientsare made to be zero, only the target hue or inter-hue area can beadjusted. For example, if coefficients Ar1 to Ar3 relating to h1 rrelating to red are set, the red hue is changed, and to vary theproportion between red and yellow, the coefficients Ary1 to Ary3relating to h2 ry are used.

Where it is intended to make linear adjustment of the hue or inter-hueareas, it is not necessary to calculate the product terms. In this case,the multipliers 8 a and 8 b in the polynomial calculator 3 shown in FIG.2, and the multipliers 12 b and 12 d, and the adders 13 a and 13 b inthe matrix calculator 4 shown in FIG. 5 may be omitted.

Furthermore, if, in the polynomial calculator 3, the values ofcalculation coefficients aq1 to aq6 and ap1 to ap6 in

-   -   h2 ry=min (aq1*h1 y, ap1*h1 r),    -   h2 rm=min (aq2*h1 m, ap2*h1 r),    -   h2 gy=min (aq3*h1 y, ap3*h1 g),    -   h2 gc=min (aq4*h1 c, ap4*h1 g),    -   h2 bm=min (aq5*h1 m, ap5*h1 b), and    -   h2 bc=min (aq6*h1 c, ap6*h1 b)        are changed so as to assume integral values of 1, 2, 4, 8, . . .        , i.e., 2^(n) (where n is an integer), multiplication can be        achieved in the arithmetic units 10 a and 10 b by bit shifting.

As apparent from the foregoing, by changing the coefficients for theproduct terms and first comparison-result data relating to specifichues, it is possible to adjust only the target hue among the six hues ofred, blue, green, yellow, cyan and magenta, and by changing thecoefficients for the second comparison-result data, it is possible tovary the colors in the six inter-hue areas of red-yellow, yellow-green,green-cyan, cyan-blue, blue-magenta, and magenta-red. The adjustment ofeach hue or inter-hue area can be achieved independently, i.e., withoutinfluencing other hues or other inter-hue areas.

Each of the foregoing product terms is a second-order calculation forchroma, and each of the first and second comparison-result data is afirst-order calculation for chroma.

Accordingly, by using the product terms, and the first and secondcomparison-result data, the non-linearity of an image printing or thelike can be varied for chroma.

Accordingly, it is possible to obtain color conversion methods or colorconversion devices which can change the conversion characteristicsflexibly, without requiring a large-capacity memory.

Further description on the operation of the color conversion deviceusing the coefficients represented by the formulae (5) and (7) will begiven. FIG. 12 to FIG. 14 show an xy chromaticity diagram showing theoperation of the color conversion device of Embodiment 1. In FIG. 12 toFIG. 14, the dotted line 21 represents the gamut of the desired colorreproduction. In FIG. 12, the triangle of the solid line 22 representsthe gamut of color reproduction (reproducible colors) of the input colorsignals Ri, Gi and Bi. Here, the input color signals may be those for acertain type of image reproducing device, such as a display device,e.g., a CRT monitor. The “desired color reproduction” may be the colorreproduction by another type of display device, or theoretical orimaginary color reproduction.

The directions of lines extending from the center of each triangle tothe vertexes and points on the sides of the triangle representrespective hues.

In the example of FIG. 12, there are differences between the colorreproduction of the input color signals and the desired colorreproduction with regard to the directions of the lines extending fromthe center of the triangle to the vertexes and points on the sides. Thismeans that the hues of the reproduced colors are different.

The color conversion device of Embodiment 1 of the invention uses thefirst comparison-result data effective for each of the six hues, and thesecond comparison-result data effective for each of the inter-hue areas.

In FIG. 13, the solid line 23 represents the gamut of the colorreproduction after the adjustment of the coefficients for the firstcomparison-result data, while the broken line 24 represents the gamut ofthe color reproduction without the adjustment of the coefficients. Aswill be seen, the hues of the color reproduction as represented by thesolid line 23 and the hues of the desired color reproduction asrepresented by the dotted line 21 coincide with each other. Thecoincidence is achieved by adjusting the coefficients for the firstcomparison-result data. However, it is noted that the gamut of the colorreproduction as represented by the solid line 23 is narrower than thegamut of the color reproduction as represented by the broken line 24(without the adjustment of the coefficients).

FIG. 14 shows the gamut 25 of the color reproduction obtained when boththe coefficients for the first comparison-result data and thecoefficients for the second comparison-result data are adjusted. Byadjusting both the coefficients for the first and secondcomparison-result data, the hues of the color reproduction asrepresented by the line 25 coincides with the hues of the desired colorreproduction, and the gamut 25 of the color reproduction obtained whenboth the coefficients for the first and second comparison-result dataare identical to the gamut (22 in FIG. 12) of the color reproductionobtained when the coefficients for the first and secondcomparison-result data are not adjusted. That is, in the colorconversion device according to Embodiment 1 of the invention, byadjusting the coefficients for the first and second comparison-resultdata, the hues can be adjusted without narrowing the gamut of the colorreproduction.

In Embodiment 1 described above, the hue data r, g, b, y, m and c, andthe maximum and minimum values β and α were calculated based on theinputted image data Ri, Gi and Bi so as to obtain the calculation termsfor the respective hues, and the image data Ro, Go, Bo are obtainedafter the calculation according to the formula (1). As an alternative,after the output image data Ro, Go, Bo are obtained, they may then beconverted to data representing cyan, magenta and yellow, by determining1's complement. In this case, the same effects will be realized.

Furthermore, in Embodiment 1 described above, most of the processing wasperformed by the hardware configuration of FIG. 1. Needless to say, thesame processing can be performed by software in the color conversiondevice, and in this case, the same effects as those of Embodiment 1 willbe provided.

According to the embodiment described above, because the coefficientscan be set and/or altered by the use of the coefficient setting unit 15,it is possible to obtain color reproducibility taking into considerationthe characteristics of the output device or the input device with whichthe color conversion device of the invention is to be used or the colorconversion characteristics preferred by the user.

The coefficients can be set freely by the user, so as to alter the colorreproducibility. This is a significant advantage because different usersprefer different color reproducibilities. The color conversioncharacteristics may be changed while observing the result of the changeby means of a display or a printer, until a desired characteristics areobtained.

Embodiment 2

In Embodiment 1, the hue data r, g, b, y, m and c, and the maximum andminimum values β and α were calculated based on the inputted image dataof red, green and blue so as to obtain the calculation terms for therespective hues, and after the matrix calculation, the image data red,green and blue were obtained. But the image data of red, green and bluemay first be converted into complementary color data of cyan, magentaand yellow, by determining 1's complement of the input image data, andthen color conversion may be executed by inputting the complementarycolor data of cyan, magenta and yellow.

FIG. 15 is a block diagram showing an example of configuration of acolor conversion device of Embodiment 2 of the present invention. Indescribing Embodiment 2, the inputted image data of red, green and blueare denoted by Rj, Gj and Bj. Reference numerals 3, 4, 5, 6, and 15denote the same members as those described with reference to FIG. 1 inconnection with Embodiment 1. Reference numeral 14 denotes a complementcalculator; 1 b, a minimum and maximum calculator for generating maximumand minimum values β and α of complementary color data and anidentification code for indicating, among the six hue data, data whichare zero; and 2 b, a hue data calculator for calculating hue data r, g,b, y, m and c based on complementary color data Ci, Mi and Yi from thecomplement calculator 14 and outputs from the minimum and maximumcalculator 1 b.

Next, the operation will be described. The complement calculator 14receives the image data Rj, Gj and Bj, and outputs complementary colordata Ci, Mi and Yi obtained by determining 1's complements. The minimumand maximum calculator 1 b outputs the maximum and minimum values β andα of each of these complementary color data and the identification codeS1.

Then, the hue data calculator 2 b receives the complementary color dataCi, Mi and Yi and the maximum and minimum values β and α from theminimum and maximum calculator 1 b, performs subtraction of

-   -   r=β−Ci,    -   g=β−Mi,    -   b=β−Yi,    -   y=Yi−α,    -   m=Mi−α, and    -   c=Ci−α,        and outputs six hue data r, g, b, y, m and c. Here, at least two        among these six hue data are zero. The identification code S1        outputted from the minimum and maximum calculator 1 b is used        for specifying, among the six hue data, data which is zero. The        value of the identification code S1 depends on which of Ci, Mi        and Yi the maximum and minimum values β and α are. Relations        between the data among the six hue data which are zero, and the        values of the identification code S1 are the same as those in        Embodiment 1, and thus further explanation will be omitted.

Then, the six hue data r, g, b, y, m and c outputted from the hue datacalculator 2 b are sent to the polynomial calculator 3, and the hue datac, m and y are also sent to the matrix calculator 4. The polynomialcalculator 3 also receives the identification code S1 outputted from theminimum and maximum calculator 1 b, and performs calculation byselecting, from the hue data, two data Q1 and Q2 which are not zero, andfrom the hue data y, m and c, two data P1 and P2 which are not of avalue zero. This operation is identical to that described with referenceto FIG. 2 in connection with Embodiment 1, so that detailed descriptionthereof is omitted.

The output of the polynomial calculator 3 is supplied to the matrixcalculator 4, and the calculation coefficients U (Fij) and fixedcoefficients U (Eij) for the polynomial data are read or outputted fromthe coefficient storage 5 in FIG. 15 based on the identification codeS1, and sent to the matrix calculator 4.

The matrix calculator 4 receives the hue data c, m and y from the huedata calculator 2 b, the polynomial data T1 to T5 from the polynomialcalculator 3 and the coefficients U from the coefficient storage 5, andoutputs the results of calculation according to the following formula(8) as image data C1, M1 and Y1. $\begin{matrix}{\begin{bmatrix}{C1} \\{M1} \\{Y1}\end{bmatrix} = {{({Eij})\begin{bmatrix}c \\m \\y\end{bmatrix}} + {({Fij})\begin{bmatrix}{T1} \\{T2} \\{T3} \\{T4} \\{T5}\end{bmatrix}}}} & (8)\end{matrix}$

In the formula (8), for (Eij), i=1 to 3 and j=1 to 3, and for (Fij), i=1to 3 and j=1 to 5.

The operation at the matrix calculator 4 is similar to that describedwith reference to FIG. 5 in connection with Embodiment 1, but theinputted hue data is c (or m, y), and C1 (or M1, Y1) is calculated andoutputted. The detailed description thereof is therefore omitted.

The synthesizer 6 receives the image data C1, M1 and Y1 from the matrixcalculator 4 and the minimum value a outputted from the minimum andmaximum calculator 1 b representing the achromatic data, performsaddition, and outputs image data Co, Mo and Yo. The equation used forobtaining the image data color-converted by the color-conversion methodof FIG. 15 is therefore given by the following formula (2).$\begin{matrix}{\begin{bmatrix}{Co} \\{Mo} \\{Yo}\end{bmatrix} = {{({Eij})\begin{bmatrix}c \\m \\y\end{bmatrix}} + {({Fij})\begin{bmatrix}{c*m} \\{m*y} \\{y*c} \\{r*g} \\{g*b} \\{b*r} \\{h1r} \\{h1g} \\{h1b} \\{h1c} \\{h1m} \\{h1y} \\{h2ry} \\{h2rm} \\{h2gy} \\{h2gc} \\{h2bm} \\{h2bc}\end{bmatrix}} + \begin{bmatrix}\alpha \\\alpha \\\alpha\end{bmatrix}}} & (2)\end{matrix}$

In the formula (2), for (Eij), i=1 to 3 and j=1 to 3, and for (Fij), i=1to 3 and j=1 to 18, and

-   -   h1 r=min (m, y),    -   h1 g=min (y, c),    -   h1 b=min (c, m),    -   h1 c=min (g, b),    -   h1 m=min (b, r),    -   h1 y=min (r, g),    -   h2 ry=min (aq1*h1 y, ap1*h1 r),    -   h2 rm=min (aq2*h1 m, ap2*h1 r),    -   h2 gy=min (aq3*h1 y, ap3*h1 g),    -   h2 gc=min (aq4*h1 c, ap4*h1 g),    -   h2 bm=min (aq5*h1 m, ap5*h1 b), and    -   h2 bc=min (aq6*h1 c, ap6*h1 b), and        aq1 to aq6 and ap1 to ap6 indicate calculation coefficients        generated by the calculation coefficient selector 11 of FIG. 2.

The difference between the number of calculation terms in the formula(2) and the number of calculation terms in FIG. 15 is that FIG. 15 showsa method of calculation for each pixel excluding the calculation termswhich are of a value zero, while the formula (2) represents a generalformula for a set of pixels. In other words, eighteen polynomial datafor one pixel of the formula (2) can be reduced to five effective data,and this reduction is achieved by exploiting a characteristic of the huedata.

The combination of effective data is changed according to image data ofthe target pixel. For all image data, all the polynomial data can beeffective.

The calculation terms outputted from the polynomial calculator based onthe formula (2) are identical to those of the formula (1) inEmbodiment 1. Thus, relations between the six hues and inter-hue areasand effective calculation terms are the same as those shown in FIG. 11Aand FIG. 11B. Therefore, as in Embodiment 1, in the coefficient storage5, by changing the coefficients for an effective calculation term for ahue or for an inter-hue area to be adjusted, only the target hue orinter-hue area can be adjusted. In addition, by changing thecoefficients in the calculation coefficient selector 11 in thepolynomial calculator 3, part of the inter-hue area where thecalculation term in the inter-hue area is effective can be changedwithout giving any influence to the other hues.

Here, an example of coefficients outputted from by the coefficientstorage 5 of Embodiment 2 are the coefficients U (Eij) of the formula(5), as in Embodiment 1. If the coefficients U (Fij) are all zero, colorconversion is not executed. Also, if those of the coefficients U (Fij)of the formula (7) which relate to the second-order calculation termswhich are product terms are all zero, adjustment is performed based onthe coefficients for the first and second comparison-result data, whichare first-order calculation terms, and linear adjustment on only a hueor an inter-hue area can be achieved. By setting coefficients relatingto a first-order calculation term for a hue or an inter-hue area to bechanged and setting other coefficients to zero, only the target hue orinter-hue area can be adjusted.

As apparent from the foregoing, by changing the coefficients for theproduct terms and first comparison-result data relating to specifichues, it is possible to adjust only the target hue among the six hues ofred, blue, green, yellow, cyan and magenta, and by changing thecoefficients for the second comparison-result data, it is possible tovary the colors in the six inter-hue areas of red-yellow, yellow-green,green-cyan, cyan-blue, blue-magenta, and magenta-red. The adjustment ofeach hue or inter-hue area can be achieved independently, i.e., withoutinfluencing other hues or other inter-hue areas.

Each of the foregoing product terms is a second-order calculation forchroma, and each of the first and second comparison-result data is afirst-order calculation for chroma.

Accordingly, by using the product term and the first and secondcomparison-result data, the non-linearity of an image-printing or thelike can be varied for chroma.

Accordingly, it is possible to obtain color conversion methods or colorconversion devices which can change the conversion characteristicsflexibly, without requiring a large-capacity memory.

Furthermore, in Embodiment 2 described above, most of the processing wasperformed by the hardware configuration of FIG. 15. Needless to say, thesame processing can be performed by software in the color conversiondevice, and in this case, the same effects as those of Embodiment 2 willbe provided.

Embodiment 3

In Embodiment 1, part of an example of configuration of the matrixcalculator 4 is as shown in the block diagram of FIG. 5, and the huedata and the respective calculation terms and the minimum value a amongthe image data Ri, Gi and Bi which is achromatic data are added togetherto produce the image data Ro, Go, Bo, as shown in the formula (1). It ispossible to adopt a configuration shown in FIG. 16 in which coefficientsfor the minimum value α which is achromatic data are outputted from thecoefficient storage and the matrix calculation is performed on theminimum value α as well, to adjust the achromatic component.

FIG. 16 is a block diagram showing an example of configuration of acolor conversion device of Embodiment 3 of the present invention. In thefigure, reference numerals 1, 2, 3, and 15 denote members identical tothose described with reference to FIG. 1 in connection withEmbodiment 1. Reference numeral 4 b denotes a matrix calculator, and 5 bdenotes a coefficient storage.

The operation will next be described. The determination of the maximumvalue β, the minimum value α, and the identification code S1 from theinputted data at the minimum and maximum calculator 1, the calculationof the six hue data at the hue data calculator 2, and the determinationof the calculation terms at the polynomial calculator 3 are identical tothose of Embodiment 1, and detailed description thereof is thereforeomitted.

The calculation coefficients U (Fij) and fixed coefficients U (Eij) forthe polynomial data are read or outputted from the coefficient storage 5b shown in FIG. 16 based on the identification code S1, and sent to thematrix calculator 4 b. The matrix calculator 4 b receives the hue datar, g, and b from the hue data calculator 2, the polynomial data T1 to T5from the polynomial calculator 3, the minimum value α from the minimumand maximum calculator 1, and the coefficients U from the coefficientstorage 5 b, and performs calculation thereon. The equation used for thecalculation, for adjusting the achromatic component as well, isrepresented by the following formula (9). $\begin{matrix}{\begin{bmatrix}{Ro} \\{Go} \\{Bo}\end{bmatrix} = {{({Eij})\begin{bmatrix}r \\g \\b\end{bmatrix}} + {({Fij})\begin{bmatrix}{T1} \\{T2} \\{T3} \\{T4} \\{T5} \\\alpha\end{bmatrix}}}} & (9)\end{matrix}$

In the formula (9), for (Eij), i=1 to 3 and j=1 to 3, and for (Fij), i=1to 3 and j=1 to 6.

FIG. 17 is a block diagram showing an example of configuration of thematrix calculator 4 b. In FIG. 17, reference numerals 12 a to 12 f and13 a to 13 f denote members identical to those in the matrix calculator4 of Embodiment 1. Reference numeral 12 g denotes a multiplier receivingthe minimum value a from the minimum and maximum calculator 1 indicatingthe achromatic component, and the coefficients U from the coefficientstorage 5 b, and performs multiplication thereon. Reference numeral 13 fdenotes an adder.

Next, the operation will be described. The multipliers 12 a to 12 freceive the hue data r, the polynomial data T1 to T5 from the polynomialcalculator 3 and the coefficients U (Eij) and U (Fij) from thecoefficient storage 5, and then output the products thereof. The adders13 a to 13 e add the products and sums. These operations are identicalto those of the matrix calculator 4 in Embodiment 1. The multiplier 12 greceives the minimum value α among the image data Ri, Gi and Bi, fromthe minimum and maximum calculator 1 which corresponds to the achromaticcomponent, and the coefficients U (Fij) from the coefficient storage 5b, and performs multiplication, and outputs the product to the adder 13f, where the product is added to the output of the adder 13 e, and thesum total is output as the image data Ro. In the example of FIG. 17, ifthe hue data r is replaced by g or b, the image data Go or Bo iscalculated.

The part of the coefficients (Eij) and (Fij) corresponding to the huedata r, g and b are used. In other words, if three configurations, eachsimilar to that of FIG. 17, are used in parallel for the hue data r, gand b, matrix calculation can be performed at a higher speed.

The equation for determining the image data is represented by thefollowing formula (3). $\begin{matrix}{\begin{bmatrix}{Ro} \\{Go} \\{Bo}\end{bmatrix} = {{({Eij})\begin{bmatrix}r \\g \\b\end{bmatrix}} + {({Fij})\begin{bmatrix}{c*m} \\{m*y} \\{y*c} \\{r*g} \\{g*b} \\\begin{matrix}{b*r} \\{h1r} \\{h1g} \\{h1b} \\{h1c} \\{h1m} \\{h1y} \\{h2ry} \\{h2rm} \\{h2gy} \\{h2gc} \\{h2bm} \\{h2bc} \\\alpha\end{matrix}\end{bmatrix}}}} & (3)\end{matrix}$

In the formula (3), for (Eij), i=1 to 3 and j=1 to 3, and for (Fij), i=1to 3 and j=1 to 19.

The difference between the number of calculation terms in the formula(3) and the number of calculation terms in FIG. 16 is that, as inEmbodiment 1, FIG. 16 shows a method of calculation for each pixelexcluding the calculation terms which are of a value zero, while theformula (3) represents a general formula for a set of pixels. In otherwords, nineteen polynomial data for one pixel of the formula (3) can bereduced to six effective data, and this reduction is achieved byexploiting a characteristic of the hue data.

The combination of effective data is changed according to image data ofthe target pixel. For all image data, all the polynomial data can beeffective.

If all the coefficients relating to the minimum value α are “1”, theachromatic data is not converted, and will be of the same value as theachromatic data in the inputted data. If the coefficients used in thematrix calculation are changed, it is possible to choose between reddishblack, bluish black, and the like, and the achromatic component can beadjusted.

As apparent from the foregoing, by changing the coefficients of theproduct term and first comparison-result data relating to specific hues,and the second comparison-result data relating to the inter-hue areas,it is possible to adjust only the target hue or inter-hue area among thesix hues of red, blue, green, yellow, cyan and magenta, and the sixinter-hue areas, without influencing other hues and inter-hue areas. Bychanging the coefficients relating to the minimum value α which is theachromatic data, it is possible to adjust only the achromatic componentwithout influencing the hue components, and choose between a standardblack, reddish black, bluish black and the like.

In Embodiment 3 described above, the image data Ro, Go and Bo areobtained after the calculation according to the formula (3). As analternative, after the output image data Ro, Go, Bo are obtained, theymay then be converted to data representing cyan, magenta and yellow, bydetermining 1's complement. If the coefficients used in the matrixcalculation can be changed for the respective hues, the inter-hue areas,and the minimum value a which is achromatic data, effects similar tothose discussed above can be obtained.

As in Embodiment 1 described above, in Embodiment 3, as well, the sameprocessing can be performed by software in the color conversion device,and in this case, the same effects as those of Embodiment 3 will beprovided.

Embodiment 4

Embodiment 2 was configured to add the hue data, the calculation terms,and the minimum value α which is achromatic data, as shown in theformula (2). As an alternative, the configuration may be such thatcoefficients for the minimum value a which is achromatic data isoutputted from the coefficient storage and the matrix calculation isperformed on the minimum value α as well, as shown in FIG. 18, so thatthe achromatic component is thereby adjusted.

FIG. 18 is a block diagram showing an example of configuration of colorconversion device according to Embodiment 4 of the invention. In thefigure, reference numerals 14, 1 b, 2 b, 3, and 15 denote membersidentical to those described with reference to FIG. 15 in connectionwith Embodiment 2, and reference numerals 4 b and 5 b denote membersidentical to those described with reference to FIG. 16 in connectionwith Embodiment 3.

The operation will next be described. The image data Rj, Gj, BJ areinput to the complement calculator 14 to obtain the complementary dataCi, Mi, Yi by the process of determining 1's complement. Thedetermination of the maximum value β, the minimum value a and theidentification code S1 at the minimum and maximum calculator 1 b, thecalculation of the six hue data at the hue data calculator 2 b, and thedetermination of the calculation terms at the polynomial calculator 3are identical to those in the case of the complementary data Ci, Mi, Yiin Embodiment 2. The detailed description thereof are therefore omitted.

The calculation coefficients U (Fij) and the fixed coefficients U (Eij)for the polynomial data are read or outputted from the coefficientstorage 5 b in FIG. 18 based on the identification code S1, and sent tothe matrix calculator 4 b.

The matrix calculator 4 b receives the hue data c, m, and y from the huedata calculator 2 b, the polynomial data T1 to T5 from the polynomialcalculator 3, the minimum value a from the minimum and maximumcalculator 1, and the coefficients U from the coefficient storage 5 b,and performs calculation thereon. The equation used for the calculation,for adjusting the achromatic component as well, is represented by thefollowing formula (10). $\begin{matrix}{\begin{bmatrix}{Co} \\{Mo} \\{Yo}\end{bmatrix} = {{({Eij})\begin{bmatrix}c \\m \\y\end{bmatrix}} + {({Fij})\begin{bmatrix}{T1} \\{T2} \\{T3} \\{T4} \\{T5} \\\alpha\end{bmatrix}}}} & (10)\end{matrix}$

In the formula (10), for (Eij), i=1 to 3 and j=1 to 3, and for (Fij),i=1 to 3 and j=1 to 6.

The operation at the matrix calculator 4 b is similar to that describedwith reference to FIG. 17 in connection with Embodiment 3, but theinputted hue data is c (or m, y), and Co (or Mo, Yo) is calculated andoutputted. The detailed description thereof is therefore omitted.

The equation for determining the image data is represented by thefollowing formula (4). $\begin{matrix}{\begin{bmatrix}{Co} \\{Mo} \\{Yo}\end{bmatrix} = {{({Eij})\begin{bmatrix}c \\m \\y\end{bmatrix}} + {({Fij})\begin{bmatrix}{c*m} \\{m*y} \\{y*c} \\{r*g} \\{g*b} \\\begin{matrix}{b*r} \\{h1r} \\{h1g} \\{h1b} \\{h1c} \\{h1m} \\{h1y} \\{h2ry} \\{h2rm} \\{h2gy} \\{h2gc} \\{h2bm} \\{h2bc} \\\alpha\end{matrix}\end{bmatrix}}}} & (4)\end{matrix}$

In the formula (4), for (Eij), i=1 to 3 and j=1 to 3, and for (Fij), i=1to 3 and j=1 to 19.

The difference between the number of calculation terms in the formula(4) and the number of calculation terms in FIG. 18 is that, as inEmbodiment 2, FIG. 18 shows a method of calculation for each pixelexcluding the calculation terms which are of a value zero, while theformula (4) represents a general formula for a set of pixels. In otherwords, nineteen polynomial data for one pixel of the formula (4) can bereduced to six effective data, and this reduction is achieved byexploiting a characteristic of the hue data.

The combination of effective data is changed according to image data ofthe target pixel. For all image data, all the polynomial data can beeffective.

If all the coefficients relating to the minimum value a are “1”, theachromatic data is not converted, and will be of the same value as theachromatic data in the inputted data. If the coefficients used in thematrix calculation are changed, it is possible to choose between reddishblack, bluish black, and the like, and the achromatic component can beadjusted.

As apparent from the foregoing, by changing the coefficients of theproduct term and first comparison-result data relating to specific hues,and the second comparison-result data relating to the inter-hue areas,it is possible to adjust only the target hue or inter-hue area among thesix hues of red, blue, green, yellow, cyan and magenta, and the sixinter-hue areas, without influencing other hues and inter-hue areas. Bychanging the coefficients relating to the minimum value a which is theachromatic data, it is possible to adjust only the achromatic componentwithout influencing the hue components, and choose between a standardblack, reddish black, bluish black and the like.

As in Embodiment 1 described above, in Embodiment 4, as well, the sameprocessing can be performed by software in the color conversion device,and in this case, the same effects as those of Embodiment 4 will beprovided.

Embodiment 5

In Embodiment 2 and Embodiment 4, the image data Ci, Mi, Yi are obtainedby determining 1's complement of input image data Rj, Gj and Bj.Similarly, the image data Ri, Gi, Bi used in Embodiment 1 may be thoseobtained by 1's complement of input image data representing cyan,magenta and yellow, Cj, Mj and Yj. For the determination of the 1'scomplement of the input image data Cj, Mj, Yj, a complement calculatorwhich is similar to the complement calculator 14 in FIG. 15 or FIG. 18but which receives the image data Cj, Mj, Yj may be used. FIG. 19 showsan example of color conversion device having such a complementcalculator denoted 14 b. Apart from the addition of the complementcalculator 14 b, the configuration of the color conversion device ofFIG. 19 is similar to the color conversion device of FIG. 1. Similarmodification may be made to the color conversion device of Embodiment 3shown in FIG. 16.

It should also be noted that the modifications described in connectionwith Embodiment 1 to Embodiment 4 can also be applied to Embodiment 5.

In the various embodiments described above, it is assumed that theinvention is applied to a color conversion device for use with an imageoutput device such as a display device or a printer. However, theinvention can also be applied to a color conversion device for use witha camera, a scanner, or other image input device, and yet the effectssimilar to those described above can be obtained.

In the various embodiments described above, the coefficient storage 5 or5 b may be in the form of a random access memory, a read-only memory, anelectrically erasable/programmable read-only memory (EEPROM), registers,or of any other configuration, as long as it can store predeterminedvalues.

Embodiment 6

When a read-only memory is used as the coefficient storage 5 or 5 b, thecoefficient setting unit 15 may not form part of the color conversiondevice, but is part of a manufacturing device. In such a case, the colorconversion device is manufactured in the following way.

First, a color conversion device which may be any one of those ofEmbodiment 1 to Embodiment 5, but which does not include the coefficientsetting unit 15, and of which the contents of the coefficient storage 5or 5 b have not been set is produced.

Then, taking into consideration the characteristics of the device (whichmay be an output device, such as a display device or a printer, or aninput device such as a camera or an image scanner) with which the colorconversion device is intended to be used, the coefficients aredetermined and written in the coefficient storage 5 or 5 a. Here, thecharacteristics of the input device or the output device in question maybe those which vary depending on the type of the device, or those whichvary depending on the manufacturing variations.

For writing the coefficients in the coefficient storage 5 or 5 b, acoefficient setting unit 15, which in this case is part of amanufacturing device, is used.

By making it possible to set the coefficients by the use of thecoefficient setting unit 15, it is possible to obtain colorreproducibility taking into consideration the characteristics of theoutput device or the input device with which the color conversion deviceof the invention is to be used.

The color conversion characteristics may be changed, while observing theresult of the change by means of a display unit, or a printer, until adesired characteristics are obtained.

When the color conversion device is used with a particular displaydevice (this includes a case where the color conversion device isintegral with the display device), it is desirable that the colorconversion characteristics are changed and the result of the change areobserved using the particular display device. Similarly, when the colorconversion device is used with a particular printer, it is desirablethat the color conversion characteristics are changed and the result ofthe change are observed using the particular printer.

In this way, the coefficients can be optimized in a short time. Thecoefficients may be set so as to be most appropriate for the particulartype of the input device or the output device, or to compensate for themanufacturing variations in the characteristics of the input device orthe output device.

Accordingly, the color conversion device according to the invention isappropriate from the view-point of mass production.

The setting and writing of the coefficients during manufacture of thecolor conversion device can be made when the coefficient storage isother than a read-only memory. In such a case, the setting and writingof the coefficients may be conducted using the coefficient setting unit15 forming part of the color conversion device or a separate unit (notshown) which has an equivalent function, but which forms part of themanufacturing device.

1. A color conversion device for performing pixel-by-pixel colorconversion from a first set of three color data representing red, greenand blue, or cyan, magenta and yellow, into a second set of three colordata representing red, green and blue, or cyan, magenta, and yellow,said device comprising: first calculation means for calculating aminimum value α and a maximum value β of said first set of three colordata for each pixel; hue data calculating means for calculating hue datar, g, b, y, m and c based on said first set of three color data, andsaid minimum and maximum values α and β outputted from said firstcalculation means; means for generating first comparison-result databased on the hue data outputted from said hue data calculating means;means for generating second comparison-result data based on said firstcomparison-result data; second calculation means for performingcalculation using the hue data outputted from said hue data calculatingmeans to produce calculation result data; coefficient storage means forstoring matrix coefficients for the hue data, the calculation resultdata, the first comparison-result data and the second comparison-resultdata; coefficient setting means for setting specified coefficients insaid coefficient storage means; and third calculation means responsiveto said hue data, said first comparison-result data, said secondcomparison-result data, said calculation result data, and thecoefficients from said coefficient storage means for calculating saidsecond set of three color data representing red, green and blue, orcyan, magenta, and yellow, said third calculation means performingcalculation including matrix calculation performed at least on said huedata, said first comparison-result data, said second comparison-resultdata, said calculation result data, and the coefficients from saidcoefficient storage means.
 2. The color conversion device according toclaim 1, wherein said third calculation means performs said matrixcalculation on said hue data, said first comparison-result data, saidsecond comparison-result data, said calculation result data, and thecoefficients from said coefficient storage means, and further includessynthesizing means for adding said minimum value α from said firstcalculation means to the results of said matrix calculation.
 3. Thecolor conversion device according to claim 2, wherein said coefficientstorage means outputs predetermined matrix coefficients Eij (i=1 to 3,j=1 to 3), and Fij (i=1 to 3, j=1 to 18), and said third calculationmeans performs the calculation using the hue data, said firstcomparison-result data, said second comparison-result data, saidcalculation result data, said minimum value α from said firstcalculation means, and said matrix coefficients to determine said secondset of three color data representing red, green and blue, denoted by Ro,Go and Bo, in accordance with the following formula (1): $\begin{matrix}{\begin{bmatrix}{Ro} \\{Go} \\{Bo}\end{bmatrix} = {{({Eij})\begin{bmatrix}r \\g \\b\end{bmatrix}} + {({Fij})\begin{bmatrix}{c*m} \\{m*y} \\{y*c} \\{r*g} \\{g*b} \\\begin{matrix}{b*r} \\{h1r} \\{h1g} \\{h1b} \\{h1c} \\{h1m} \\{h1y} \\{h2ry} \\{h2rm} \\{h2gy} \\{h2gc} \\{h2bm} \\{h2bc}\end{matrix}\end{bmatrix}} + \begin{bmatrix}\alpha \\\alpha \\\alpha\end{bmatrix}}} & (1)\end{matrix}$ wherein h1 r, h1 g, h1 b, h1 c, h1 m and h1 y denote saidfirst comparison-result data, and h2 ry, h2 rm, h2 gy, h2 gc, h2 bm andh2 bc denote said second comparison result data.
 4. The color conversiondevice according to claim 2, wherein said coefficient storage meansoutputs predetermined matrix coefficients Eij (i=1 to 3, j=1 to 3), andFij (i=1 to 3, j=1 to 18), and said third calculation means performs thecalculation using the hue data, said first comparison-result data, saidsecond comparison-result data, said calculation result data, saidminimum value α from said first calculation means, and said matrixcoefficients to determine said second set of three color datarepresenting cyan, magenta and yellow denoted by Co, Mo and Yo, inaccordance with the following formula (2): $\begin{matrix}{\begin{bmatrix}{Co} \\{Mo} \\{Yo}\end{bmatrix} = {{({Eij})\begin{bmatrix}c \\m \\y\end{bmatrix}} + {({Fij})\begin{bmatrix}{c*m} \\{m*y} \\{y*c} \\{r*g} \\{g*b} \\\begin{matrix}{b*r} \\{h1r} \\{h1g} \\{h1b} \\{h1c} \\{h1m} \\{h1y} \\{h2ry} \\{h2rm} \\{h2gy} \\{h2gc} \\{h2bm} \\{h2bc}\end{matrix}\end{bmatrix}} + \begin{bmatrix}\alpha \\\alpha \\\alpha\end{bmatrix}}} & (2)\end{matrix}$ wherein h1 r, h1 g, h1 b, h1 c, h1 m and h1 y denote saidfirst comparison-result data, and h2 ry, h2 rm, h2 gy, h2 gc, h2 bm andh2 bc denote said second comparison result data.
 5. The color conversiondevice according to claim 1, wherein said third calculation meansperforms said matrix calculation on said hue data, said firstcomparison-result data, said second comparison-result data, saidcalculation result data, the coefficients from said coefficient storagemeans, and said minimum value α from said first calculation means. 6.The color conversion device according to claim 5, wherein saidcoefficient storage means outputs predetermined matrix coefficients Eij(i=1 to 3, j=1 to 3), and Fij (i=1 to 3, j=1 to 19), and said thirdcalculation means performs the calculation using the hue data, saidfirst comparison-result data, said second comparison-result data, saidcalculation result data, said minimum value α from said firstcalculation means, and said matrix coefficients to determine said secondset of three color data representing red, green and blue, denoted by Ro,Go and Bo, in accordance with the following formula (3): $\begin{matrix}{\begin{bmatrix}{Ro} \\{Go} \\{Bo}\end{bmatrix} = {{({Eij})\begin{bmatrix}r \\g \\b\end{bmatrix}} + {({Fij})\begin{bmatrix}{c*m} \\{m*y} \\{y*c} \\{r*g} \\{g*b} \\\begin{matrix}{b*r} \\{h1r} \\{h1g} \\{h1b} \\{h1c} \\{h1m} \\{h1y} \\{h2ry} \\{h2rm} \\{h2gy} \\{h2gc} \\{h2bm} \\{h2bc} \\\alpha\end{matrix}\end{bmatrix}}}} & (3)\end{matrix}$ wherein h1 r, h1 g, h1 b, h1 c, h1 m and h1 y denote saidfirst comparison-result data, and h2 ry, h2 rm, h2 gy, h2 gc, h2 bm andh2 bc denote said second comparison result data.
 7. The color conversiondevice according to claim 5, wherein said coefficient storage meansoutputs predetermined matrix coefficients Eij (i=1 to 3, j=1 to 3), andFij (i=1 to 3, j=1 to 19), and said third calculation means performs thecalculation using e hue data, said first comparison-result data, saidsecond comparison-result data, said calculation result data, saidminimum value α from said first calculation means, and said matrixcoefficients to determine said second set of three color datarepresenting cyan, magenta and yellow denoted by Co, Mo and Yo, inaccordance with the following formula (4): $\begin{matrix}{\begin{bmatrix}{Co} \\{Mo} \\{Yo}\end{bmatrix} = {{({Eij})\begin{bmatrix}c \\m \\y\end{bmatrix}} + {({Fij})\begin{bmatrix}{c*m} \\{m*y} \\{y*c} \\{r*g} \\{g*b} \\\begin{matrix}{b*r} \\{h1r} \\{h1g} \\{h1b} \\{h1c} \\{h1m} \\{h1y} \\{h2ry} \\{h2rm} \\{h2gy} \\{h2gc} \\{h2bm} \\{h2bc} \\\alpha\end{matrix}\end{bmatrix}}}} & (4)\end{matrix}$ wherein h1 r, h1 g, h1 b, h1 c, h1 m and h1 y denote saidfirst comparison-result data, and h2 ry, h2 rm, h2 gy, h2 gc, h2 bm andh2 bc denote said second comparison result data.
 8. The color conversiondevice according to claim 1, wherein said first set of three color datarepresent red, green and blue, said second set of three color datarepresent red, green and blue, and said hue data calculation meanscalculates the hue data r, g, b, y, m, c by subtraction in accordancewith: r=Ri−α, g=Gi−α, b=Bi−α, y=β−Bi, m=β−Gi, and c=β−Ri, wherein Ri, Giand Bi represent said first set of three color data.
 9. The colorconversion device according to claim 1, wherein said first set of threecolor data represent cyan, magenta and yellow, said second set of threecolor data represent red, green and blue, said color conversion devicefurther comprises means for determining a complement of said first setof three color data, and said hue data calculation means calculates thehue data r, g, b, y, m, c by subtraction in accordance with: r=Ri−α,g=Gi−α, b=Bi−α, y=β−Bi, m=β−Gi, and c=β−Ri, wherein Ri, Gi and Birepresent data produced by the determination of the complement of saidfirst set of three color data.
 10. The color conversion device accordingto claim 1, wherein said first set of three color data represent cyan,magenta and yellow, said second set of three color data represent cyan,magenta and yellow, and said hue data calculation means calculates thehue data r, g, b, y, m, c by subtraction in accordance with: r=β−Ci,g=β−Mi, b=β−Yi, y=Yi−α, m=Mi−α, and c=Ci−α. wherein Ci, Mi and Yirepresent said first set of three color data.
 11. The color conversiondevice according to claim 1, wherein said first set of three color datarepresent red, green and blue, said second set of three color datarepresent cyan, magenta and yellow, said color conversion device furthercomprises means for determining a complement of said first set of threecolor data, and said hue data calculation means calculates the hue datar, g, b, y, m, c by subtraction in accordance with: r=β−Ci, g=β−Mi,b=β−Yi, y=Yi−α, m=Mi−α, and c=Ci−α. wherein Ci, Mi and Yi represent dataproduced by the determination of the complement of said first set ofthree color data.
 12. The color conversion device according to claim 1,wherein said first comparison-result data generating means determinesthe comparison-result data among the hue data r, g and b, and thecomparison-result data among the hue data y, m and c, and said secondcomparison-result data generating means comprises multiplying means formultiplying the first comparison-result data outputted from said firstcomparison-result data generating means with specific calculationcoefficients, and means for determining the comparison-result data basedon the outputs of said multiplication means.
 13. The color conversiondevice according to claim 12, wherein said first comparison-result datagenerating means determines the first comparison-result data: h1 r=min(m, y), h1 g=min (y, c), h1 b=min (c, m), h1 c=min (g, b), h1 m=min (b,r), and h1 y=min (r, g), (with min (A, B) representing the minimum valueof A and B), said second comparison-result data generating meansdetermines the second comparison-result data: h2 ry=min (aq1*h1 y,ap1*h1 r), h2 rm=min (aq2*h1 m, ap2*h1 r), h2 gy=min (aq3*h1 y, ap3*h1g), h2 gc=min (aq4*h1 c, ap4*h1 g), h2 bm=min (aq5*h1 m, ap5*h1 b), andh2 bc=min (aq6*h1 c, ap6*h1 m).
 14. The color conversion deviceaccording to claim 12, wherein said multiplying means in said secondcomparison-result data generating means performs calculation on saidfirst comparison result-data and said calculation coefficients bysetting said calculation coefficients aq1 to aq6 and ap1 to ap6 tointegral values of 2^(n), with n being an integer, and by bit shifting.15. The color conversion device according to claim 1, wherein saidsecond calculation means determines products of the hue data.
 16. Thecolor conversion device according to claim 1, wherein each of said firstcomparison-result data is determined from two of the hue data and iseffective for only one of the six hues of red, green, blue, cyan,magenta and yellow.
 17. The color conversion device according to claim1, wherein each of said second comparison-result data is determined fromtwo of the first comparison-result data and is effective for only one ofthe six inter-hue areas of red-yellow, yellow-green, green-cyan,cyan-blue, blue-magenta, and magenta-red.
 18. The color conversiondevice according to claim 1, wherein said coefficient storage meansoutputs specified matrix coefficients Eij (i=1 to 3, j=1 to 3) based ona formula (5) below: $\begin{matrix}{({Eij})\begin{bmatrix}1 & 0 & 0 \\0 & 1 & 0 \\0 & 0 & 1\end{bmatrix}} & (5)\end{matrix}$ and outputs the matrix coefficients Fij (i=1 to 3, j=1 to18, or j=1 to 19) such that, of the coefficients Fij, the coefficientsfor said calculation result data are set to zero, and other coefficientsare set to specified values.
 19. The color conversion device accordingto claim 1, wherein said first calculation means calculates a maximumvalue β and a minimum value α using said first set of three color data,and generates an identification code indicating the hue data which is ofa value zero, and said second calculation means performs arithmeticoperation on said hue data based on the identification code outputtedfrom said first calculation means, said coefficient storage meansoutputs said matrix coefficients based on the identification codeoutputted from said first calculation means, and said third calculationmeans performs matrix calculation using the coefficient from saidcoefficient storage means to produce said second set of three color databased on the identification code outputted from said first calculationmeans.
 20. A method of manufacturing a color conversion device which isfor use with an input or output device and which performs pixel-by-pixelcolor conversion from a first set of three color data representing red,green and blue, or cyan, magenta and yellow, into a second set of threecolor data representing red, green and blue, or cyan, magenta, andyellow, said color conversion device comprising: first calculation meansfor calculating a minimum value α and a maximum value β of said firstset of three color data for each pixel; hue data calculating means forcalculating hue data r, g, b, y, m and c based on said first set ofthree color data, and said minimum and maximum values a and B outputtedfrom said first calculation means; means for generating firstcomparison-result data based on the hue data outputted from said huedata calculating means; means for generating second comparison-resultdata based on said first comparison-result data; second calculationmeans for performing calculation using the hue data outputted from saidhue data calculating means to produce calculation result data;coefficient storage means for providing coefficients for the hue data,the calculation result data, the first comparison-result data and thesecond comparison-result data; and third calculation means responsive tosaid hue data, said first comparison-result data, said secondcomparison-result data, said calculation result data, and thecoefficients from said coefficient storage means for calculating saidsecond set of three color data representing red, green and blue, orcyan, magenta, and yellow, said third calculation means performingcalculation including matrix calculation performed at least on said huedata, said first comparison-result data, said second comparison-resultdata, said calculation result data, and the coefficients from saidcoefficient storage means, said method comprising the steps of: (a)producing the color conversion device which includes the above-recitedelements, but in which said coefficients are not stored in saidcoefficient storage means; and (b) writing said coefficients to saidcoefficient storage means on the basis of characteristics of the inputor output device with which the color conversion device is to be used.